In recent years, as a method of mobile wireless communication, the MIMO (Multiple-Input Multiple-Output) method, which uses multiple antennas, has begun to be used for transmission and reception of a wireless signal. Especially, if using MIMO-multiplexed transmission for orthogonal frequency division multiplexing (OFDM) access, MIMO demodulation becomes easier. This is because a signal separation process can be implemented with high accuracy without being influenced by multipath interference.
Concrete wireless communication methods that use MIMO-multiplexed transmission for OFDM access include the LTE (Long Term Evolution).
Various methods have been proposed for signal separation technologies in the MIMO technology.
Among the signal separation technologies in the MIMO technology, it is considered practical to adopt an MLD (Maximum Likelihood Detection) method. This is because a better characteristic is obtained by executing a demodulation process using an MLD method than by executing the demodulation process using other signal separation technologies. However, there is a problem that the amount of calculation is considerable.
As one of the signal separation technologies, another MLD method is known that reduces the amount of calculation while avoiding degradation of the characteristic (see, for example, Non-Patent Document 1). Therefore, it is considered that implementation of the signal separation technology using the MLD method may become popular in user terminals.
Also, as a signal separation technology in the MIMO technology, an MMSE (Minimum Mean Square Error) method is proposed to be used for the demodulation process. This is because the amount of calculation is less when executing the demodulation process using an MMSE method than when executing the demodulation process using an MLD method. However, the characteristic is inferior to those obtained by the demodulation process using an MLD method.
Therefore, it is preferable to adopt an MLD method if the characteristic is prioritized over the amount of calculation.